More than 1,650 cases of Zika have been diagnosed in the US, but this is understood to be the first time the disease has been spread by local insects, rather than as a result of foreign travel or sexual contact.

Zika causes only a mild illness in most people, but the infection in pregnant women has been strongly linked to foetal microcephaly, or abnormal smallness of the head in babies, and other severe birth defects.

Florida has now announced more aggressive mosquito-control efforts, although the evidence from South America, where the outbreak started, is that these have limited benefit.

The state is now listed by PHE as having a moderate risk rating for the Zika virus, putting it in the same category as Indonesia, the Philippines and Guinea-Bissau.

But US authorities have been keen to assure tourists that Florida is a safe place to visit.

The PHE advice is based on a list of countries and territories with current active Zika virus transmission as classified by the European Centre for Disease Control.

The virus is casting a shadow over the Rio Olympic Games, which begin next weekend, with a spate of athletes such as golfer Rory McIlroy and tennis player Tomas Berdych pulling out of the Games over fears of the virus.